c/2396: ARM/thumb 5th function argument access problem

[ted@arraycomm.com]

>Number:         2396
>Category:       c
>Synopsis:       ARM/thumb 5th function argument access problem
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Mar 26 16:26:00 PST 2001
>Closed-Date:
>Last-Modified:
>Originator:     Ted Merrill, ArrayComm, Inc.
>Release:        2.95.2
>Organization:
>Environment:
solaris 2 host, ARM/thumb (thumb-coff) target
>Description:
gcc 2.95.2 for ARM/thumb (thumb-coff) target, solaris host.
When using default optimization (-O), leaf functions
with moderate complexity and more than four word-size 
arguments are coded such that the fifth and successive
arguments are accessed at the wrong place in the stack
(specifically, 4 bytes too high).
The problem goes away if optimization is turned off 
entirely or if -fno-omit-frame-pointer is used.

This problem also appears in 2.7-armT-980223 which we
obtained a few years ago (but we didn't used to use
so many arguments to functions).

>How-To-Repeat:
Compile with -O and -S .... and note how the argument
"a4" is accessed.

int f;
int bar( int a0, int a1, int a2, int a3, int a4 ) {
    // Bug: the following gets accessed at [sp,#4] instead of [sp,#0]
    return ( f ? a4 : 0 );
}
// For reference, here is something that calls bar
int foo(void) {
    return bar(0,1,2,3,4);
}

The generated code accesses "a4" as
	ldr  r1, [sp, #4]
however, it was passed as [sp] and the stack pointer
is not modified in this optimized leaf function.
>Fix:
(unknown)
>Release-Note:
>Audit-Trail:
>Unformatted:
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